Telephone system



' July 2, 1940.

VOLUME CONTROL H. ALLEN TELEPHONE SYSTEM Filed March 1, 1939 /NVLNTOR L.H. ALLEN er ATTORNEY Patented July 2, 1940 UNITED STATES {PATENT oFFrcs Bell Telephone Laboratories,

Incorporated;

" New York, N. Y., a corporation of New York Application March 1, 1939, Serial No. 259,084'

11 Claims.

This invention relates to telephone systems and particularly to intercommunicating telephone and signal systems of the type in which loud-speakers and distant talking transmitters are employed at one or more of the substations.

It is the object of this invention to provide an improved system of intercommunication between a master station equipped with a loud-speaker and a distant talking transmitter and a subordinate station equipped with a standard hand telephone set.

This object is attained in accordance with a feature of the invention by the provision of switching means at a master station which func- 16 tions to disconnect a regular telephone set from a central ofiice line and connect it to an intercommunicating line and simultaneously disconnect a loud-speaker set from the intercommuni-' eating line whereby the regular telephone equipment at the master station may be employed for intercommunication with a subordinate station independent of the loud-speaker equipment usually employed for such purpose.

Another feature of the invention resides in the use of a pilot signal at the master station which functions upon the conjoint operation of a switch at the master station and the receiver switchhook contacts at a subordinate station" to indicate to the subscriber at the master station that the 3o subordinate subscriber is connected to the inter-- communicating line. This feature precludes the possibility of a subordinate listening in on a conversation being carried on at the master station when the subscriber thereat has inadvertently 35 failed to-restore his talk switch at the termination of a previous telephone conversation.

:These and other features of the invention will by virtue of which a subscriber at the subordinate station may signal the master station by way of 50 the loud-speaker thereat.

-The first descriptive portion will be directed to the origination of a call at the master station M employing the loud-speaking equipment.

The subscriber at the master station M having 55 operated the switch 10 in the amplifier extension.

ductor 31, contact 38 of key A, conductor 33 to (or. fur-1) cord ll to energize the amplifier schematically shown at l2, operates switch l3 which, in practice, is located on the face of the loud-speaker cabinet, to the signaling position, which. is the extreme right position on thedrawing. The 5 buzzer l4 located at the subordinate station S thereupon operates in an obvious circuit which includes the battery l5. The master station subscriber then actuates the switch l3 to contact I8 which is the talking position of the switch. With 10 L the switch l3 in the talking position, a circuit is prepared for supplying battery to the distant talking transmitter I! located at the master station M and battery I5 is connected to the master station end of the intercommunicating line L. 15

In answer to the operation of the buzzer M, the subscriber at subordinate station S removes the handset l8 from its mounting, causing current to traverse a path extending from the upper terminal of battery 15, switch 13 and. contact I 6, 20 ballast lamp l9, left winding of relay 20, line winding 2| of hybrid coil H, conductor 22 of intercommunicating line L, upper normal contacts of key 23, conductor 24, through the closed subscribers station loop, conductor 25, lower normal contacts of key 23, conductor 26 of intercommunicating line L, winding '21 of hybrid coil H,

conductor 28, right winding of relay 20, ballast lamp 29 to the other terminal of battery l5. Relay 20 operates in this circuit and in attracting its 30 armature completes the circuit to supply transmitter current to thedistant talkingtransmitter I! and causes lamp 3|! to be lighted. The transmitter supply -circuit extends from the upper terminal of battery l5, armature and front con tact of relay 20, resistance 3|, right winding of impedance coil 32, resistance 33, left winding of impedance coil 32, through the network including resistance and ballast lamps and 36, conthe other terminal of battery I5. The potential across resistance 33 supplies transmitter I! which, with the lower windings of hybrid coil H, are connected across resistance 33, The circuit for lamp 30 extends from the upper terminal of battery I5, switch l3 and contact'lli, armature and front contact of relay 20, filament of lamp to conductor 31 and thence over the circuit previously traced to the other terminal of battery I5. With =re1ay 20 operated andthe distant talking transmitter I! therefore supplied with talking battery, two-way conversation may be carried on between the subscribers at-stations M and S by way of the intercommunicating line L, if; being understood that the loud-speaker 4| and the distant talkingtransmitter [1 are connected to the line L by way of the hybrid coil H, as illustrated.

Upon completion of conversation, the subscriber at the master station restores the switch I3 to the o position, which it occupies in the drawing, and the subordinate subscriber replaces the handset l8 to its mounting. When this occurs, relay 20 releases its armature, opening the battery'supply lead to the distant talking transmitter l1 and to the lamp 30, which becomes extinguished.

It will be observed that, if after the termination of conversation on the connection just described, the subscriber at station M should inadvertently fail to restore the switch it) to off position, the battery l would remain connected to the armature of relay 20 and to the master station end of intercommunicating line L so that, should the subordinate subscriber remove the handset l8 from its mounting, relay 2!] would operate to complete the battery connection to the distant talking transmitter I1 with the recult that any conversation being carried on at station M would be picked up by the transmitter.

I1 and transmitted over line L to be overheard by the subscriber at station S. The operation of relay 20, however, also completes the circuit to lamp 30 so that the subscriber at station M would be immediately advised by the lighting of the lamp 30 that the switch l3 was left in the talking position and that the subscriber at station S, who may be the secretary of the subscriber at station M, could hear the conversation being carried on at station M. The master subscriber could then restore the key l3 to the "ofi position to disconnect the battery supply from the transmitter l1 and from lamp 30.

At 44 is diagrammatically represented a.volumecontrol which would be mounted on the face of the loud-speaker cabinet and which provides loud-speaker volume control. This control may take any desirable form, for example, the control switch may be designated as having three positions, high, medium and low. In the high position there would be no shunt resistance connected across the input of theamplifler 4|, in the medium position a suitable resistance, 300 ohms, for example, would be connected across the amplifier input-and in the low position a lower resistance, such as 100 ohms, would be. connected across the amplifier input. By

means of this volume control, the output of loud-speaker 4| may be adjusted to desired cept' for the fact the battery feed relay 2!! re-.

leases when'the subordinate handset is replaced on its mounting and immediately opens the circuit to the distant talking transmitter. In this manner,- singing or howling is prevented.

The next descriptive portion is directed to the origination of a call at the master station M employing the handset '50.

When the subscriber at the master station deaaca'sss sires to employ the hand telephone on the intercommunicating line, the key A is operated,

thereby removing the handset from the telephone line T which terminates at a central ofllce or private branch exchange and connecting it to the intercommunicatin'g line L. This transfer is eifected by the springs 5| and 52 of switch A. With the handset 50 removed from its mounting, relay 20 operates from battery l5 by way of contacts 55 of key A but performs no closure of contacts 53, and by opening the contacts 54 the key A opens the input circuit to the amplifier. At contact 38 of switch A the battery supply circuit to the distant talking transmitter l1 and to lamp 30 is opened. At contact 55 a path is closed to supply talking battery to the intercommunicating line L irrespective of the position of key l3.

The subscriber at station M then actuates the key I3 to the signaling position, causing the buzzer H at station S to operate in a circuit previously traced.

When the subordinate subscriber at station S hears the buzzer [4, the handset 18 is removed from its mounting and conversation is carried on. between the stations M and S by way of the intercommunicating line L, with both parties employing their respective telephone handsets. When conversation has been completed, the

handsets at .both stations are restored to their v respective mountings.

Thenext descriptive portion is directed to the origination of a call at the subordinate station S and intended for the subscriber at the master station M.

When the subscriber at station 8 desires to signal the master station M, the key 58 is operated, completing an obvious circuit for the buzzer 59 at station M. The key 58, in practice, would constitute an integral part of the key 23 and would operate to a non-locking'position thereof. The subscriber at station M responds to the buzzer signal by operating the key N to the talking position, contact 16. With the handset ID at station S removed from its mounting and with key l3 at station M operated to contact l6, relay 20 is operated and the distant talking transmitter I! is supplied with talking battery from the source l5 and lamp 3!! is lighted in a manner previously described. 1 Conversation takes place with the subscriber at station S empioying the handset l8 and the subscriber at station M using the distant talking transmitter I1, speech currents incoming to station M being transmitted over the intercommunicating line L, amplified by the amplifier l2 and received by the loud-speaker 4l. Upon completion of the conversation, the subscriber at station M restores the key l3 to the oif position and the subordinate subscriber at station Sregyaces the handset l8 on its mounting, thereby releasing relay 20 which, in turn, opens the battery supply to the distant talking transmitter and to the lamp 30.

' i If desirable, the subscriber at station M, upon receipt of a buzzer signaLmay employ the handset in answering the call originated at the station S merely by actuating key A.

As illustrated in the drawing, the handset at the station M is normally connected to the central oflice or private branch exchange line T by way of the normal contacts of key A associated with the springs BI and 52 thereof. With key A in norline.

mal position, as illustrated, the hand telephone functions in the well-known manner in initiating a call to the central oflice or private branch exchange over line T.- When the key A is operated to transfer the handset 50 from the line T to the intercommunicating line. L, as previously oescribed, the line ringer 10 remains bridged across the line T so that even though the handset 50 is being used on the intercommunicating line L, signals identifying calls originated at the central oflice or private branch exchange and intended for station M may be received.

The handset l8 at the subordinate station S is normally connected to the intercommunicating ofiice or private branch exchange line P, the key 23 must be operated and when this occurs, the telephone functionsin the usual manner. The ringer 12 at the subordinate station is always associated with the line P for the receipt of call signals incoming from the central oflice or private branch exchange.

With reference to Fig. 2, it will be noted that the lead extending from the lower terminal of ballast lamp I 9 is carried directly to the upper terminal of battery l5 rather-than to the switch contact I6, as in Fig. 1. With this wiring arrangement, the subscriber at the subordinate station S need only remove the telephone from its mounting and talk into the transmitter to signal the subscriber at station M by means 'of a voice signal. This obviates the necessity for the subscriber at the subordinate station actuating a Signaling key 58 in signaling the master station;

Though but one subordinate station is illustrated in the drawing, it is apparent that multiple connections for more than one such station may be provided to effect a conference service. When the system embraces a plurality of subordinate stations, the various stations will be signaled from the master station by means of code signaling.

What is claimed is:

1. In a combined telephone and loud-speaking intercommunicating system, a master station having a handset telephone normally connected to a central ofiice line, a subordinate station, an intercommunicating line interconnecting said master station and said subordinate station, a loud-speaker at'said master station normally connected to said intercommunicating line and switching means at said master station for disconnecting the handset thereat from the central ofiice line and connecting it to 'said intercommunicating line and for simultaneously opening the connection of said loud-speaker to said intercommunicating line and short-circuiting the input to the loud-speaker.

2. In -a combined telephone and loud-speaking intercommunicating system, a master station having a handset telephone normally connected to a central office line, asubordinate station, an intercommunicating line interconnecting said stations, a loud-speaker at said master station normally connected to said intercommunicating line and switching means at said master station for disconnecting the handset thereat from the central oflice line and connecting it to said'intercommunicating line and for simultaneously disinterconnecting said stations, a signal at said master station, aswitch at said master station In order to associate it with the central j and means responsive to the conjoint operation of said switch at'said master station and the receiver switchhook contacts at said subordinate station for operating said signal.

4. In a combined telephone and loud-speaking intercommunicating system, a master station, a

master station and means controlled over said intercommunicating line jointly from said master station and said subordinate station for operating said signal; v I

5. In a combined telephone and loud-speaking intercommunicating system, amaster station, a subordinate station having a telephone handset, a distant ,talking transmitter at said master sta tion, a course of current, means at said master station for preparing a supply circuit from said source of current to said distant talking transmitter, and means controlled by the receiver of the telephone handset at said subordinate station for completing the supply circuit to said transmitter.

6. In a combined telephone exchange and loudspeaking intercommunicating system, a master station, a subordinate station, an intercommunicating line interconnecting said stations, a dis-- tant talking transmitter and a signal at said master station, means controlled at said master station for preparing energizing circuits for said transmitter and said signal, a call signal at said 1 ter and said signal.

7. In a combined telephone and loud-speaking intercommunicating system, a first station, a second station, an intercommunicating line circuit interconnecting said stations and terminating at one station in the line windings by a hybrid coil, a distant talking transmitter at said first'station inductively associated with one of the line windings. of the hybrid coil, a telephone handset at said second station, a relay having windings included in circuit with the line windings of said hybrid coil and whose energizing circuit is normally open at both said stations, switching means at said first station for partially completing the energizing circuit for said relay, means responsive to the removal of said handset at said second station for completing the energizing circuit to said relay whereupon said relay operates, and means controlled by said relay for energizing said distant talking transmitter.

8. In a combined telephone and loud-speaking intercommunicating system, a first station, a-

second station, an intercommunicating line interconnecting said stations, a signal at one of said stations, and means controlled over said intercommunicating line jointly from both said stations for operating said signal.

9. In a combined telephone and loud-speaking intercommunicating system, a calling station having a distant talking transmitter, a called station, a source of supply current for said transmitter, an intercommunicating line interconnecting said stations, a switch at said calling station for connecting said source of current to said intercommunicating line, and means under the control of said called station when said switch is operated for connecting said source of supply current to the transmitter at said calling station,

said means being controlled over said intercommunicating line.

10. In a combined telephone and loud-speaking intercommunicating system, a master station equipped with a loud-speaking telephone'set master station, an intercommunicating line interconnecting said stations, means responsive to the joint operation of said switch atsaid master station and the removal of the handset atsaid subordinate station for efieetively connecting said battery to said distant talking transmitter and to said intercommunicating line to permit two-way conversation to be carried on over said intercommunicating line by means of the loudspeaking telephone set atsaid master station and the handset at said subordinate station, a telephone handset at said master station and a key thereat for disabling'the loud-speaker and distant talking transmitter at said master station and for connecting said battery to said intercommunicating line irrespective of whether or not said switch at saidmaster station is operated whereby the handset at said master station may be employed to the exclusion of said loud-speaking'set for conversation purposes on said intercommunicating line.

intercommunicating system, a master station, a

subordinate station, an intercbmmunicating lineinterconnecting said stations, said intercommunicating line including the line windings of a hybrid coil, 'a loud-speaker bridged across the coil side terminals of the line windings of'said hybrid coil, a distant talking transmitter inductively coupled to one of the line windings of said hybrid coil, a battery for supplying currentto said transmitter, switching means at both said stations which, when operated jointly, eii'ectively connect said battery to said distant talking transmitter whereupon two-way conversation may be carried on over said intercommunicating line between said stations, a telephone handset at said master station and a manually operated key at said master station for connecting said handset to said intercommunicating line, for opening the battery supply to said distant talking transmitter, for short-circuiting theinput circuit of said loud-speaker and for connecting said battery to the terminals of the line windings of said hybrid coil whereby two-way conversation may be carried on over said intercommunicating line by means of the telephone handset at said master station independently of the loud-speaker and distant talking transmitter thereat.

LAWRENCE H. ALLEN.

B 1 50 LA iii/[F R? dated July 2,1940. Dis'claimef filedJanaary;-15, '194 1,-by the assignee,

. Bell Telephone Laboratories, Inborpo'rated; A 1 Hereb enters this disclaimrto claims 3, 4, and -8 of said atent.- Gaze tte February 8, 1944.]

' DISCLAIMER 2,206,385.Lawrence H. Allen, Summit, N. J. TELEPHONE SYSTEM. Patent dated illy 2, 1940. Disclaimer filed July 22, 1942, by the a'ssignee, Bell Telephone Laboratories, Incorporated. V D. -Hereby enters this disclaimer to claims 5 and 9 of said atent. [Oflicial Gazette August 25, 1.942.] 

